HDMI (high definition multimedia interface) is a compact audio/video interface for transmitting uncompressed digital data. An HDMI connection is a DC open drain connection between a transmitter and a receiver respectively. An example of an HDMI transmitter/receiver can be seen in FIG. 1.
In FIG. 1, a transmitter 110 comprises a differential pair of open drain transistors 111 which transmit differential data over lines TX+ 140 and TX− 150 to a receiver 120 over the channel 130. The transistors 111 draw current from a voltage source AVcc 121 of the receiver and a voltage drop across terminating resistors 123 and 122 is used to determine the transmitted data. A current source 112 is used to determine the current drawn from the receiver which may be 10 mA in accordance with the HDMI specification. HDMI also specifies that the AVcc supply voltage 121 at the receiver 120 is 3.3 volts with a +/−5% tolerance.
In order to comply with the HDMI specification, current technologies may require thick gate oxide layers or the application of a level shift to prevent the active regions of a CMOS transistor from directly experiencing the 3.3 volts. The manufacturing of thicker gate oxide layers may be problematic because of the expense and the thicker layers reduce a maximum switching rate of the transistor. Level shifting may limit the switching rate of a circuit. Level shifting may further require additional current drain circuitry to prevent the level shift transistors from becoming inactive, and this may increase power consumption.
Moreover in advanced technologies it may be difficult to provide 3.3V capabilities. For example the basic components of 40 nM, 32 nM and 20 nM technology may only handle about 1V, and thicker gate components in these technologies may be unable to handle the 3.3V required by the HDMI specification.